- Books Name
- CBSE Class 7 Science Book
- Param Publication
- CBSE Class 7
Sunlight White or Coloured :
There are many phenomenons in which we can see sunlight is white or coloured. The followings are given below :
(a) Rainbow :
White light is composed of seven colours, e.g., violet, indigo, blue, green, yellow, orange and red. Phenomenon of appearance of rainbow in the sky is a proof of seven colours. A rainbow appears usually after rain in the morning or evening when the sun is low in the sky. It is formed when white light.from the sun passes through tiny prism-like water droplets and splits into different colours. -This phenormeon of splitting of white light into several different component of colors is called dispersion of light. A rainbow is arch-shaped. There are seven colours in the rainbow which gradually change from one to another. The set of colours formed on splitting of white light is called the spectrum of white light. They are seen in the order VIBGYOR, i.e., violet, indigo, blue, green, yellow, orange and red.
Since white light splits into seven colours, we should be able to get white light by mixing the seven colours ofa rainbow.
(b) Glass prism :
If we take a glass prism, and put a narrow beam of sunlight through a small hole in the window of a dark room, so, we can easily see a colourful band on the paper or screen or wall.
This shows that light consists of seven colours. If we take another prism and place it in upside down position with respect to first prism, we again get a beam of white light.
(c) Newton's Disc :
The famous English physicist Sir Isaac Newton for the first time explained this phenomenon of mixing. To prove his point, he made a disc on which the seven colours of the rainbow were painted in equal sections as shown in figure. When' this disc was rotated, all the colours disappeared and white colour appeared. This is because when the disc spins fast, all the colours pass through a spot rapidly one followed by the other. This gives the effect of putting all the colours together in one place. The colours mix and appear white. Such a disc is popularly known as Newton's disc.
On the basis of these experiments it is confirmed that white light is made of seven colours (VIBGYOR).